New fossils of the early Miocene stem-cervid Acteocemas (Artiodactyla, Ruminantia) from the Iberian Peninsula shed light on the evolutionary origin of deer antler regeneration

ABSTRACT

Acteocemas, a very poorly documented early Miocene stem-cervid, is one of the first ruminants bearing antler-like appendages, which has provided a ground for discussion on the origin of antlers. We describe a new and very complete appendage from the site of Sant Andreu de la Barca (Spain) together with some other unpublished specimens from the nearby Costablanca attributed to Acteocemas aff. infans, compare with fossils from elsewhere in Europe (including the A. infans holotype), and perform micro-CT scans. The findings provide new empirical data that Acteocemas protoantlers were able to be cast and re-grown. However, microstructural analyses suggest that the protoantler lifespan could be longer than that of modern antlers, preventing it from assuming a similar cycle. Results support that increased seasonality associated with a drop in global temperatures played a role in the origin of antler regeneration, and that deciduousness (through bone shedding) was an efficient way for (male)deer to reduce the seasonal leftover of bone mass. The early evolution of deciduousness, as in the probable irregular protoanter cycle of Acteocemas, was limited by the warming ca. 17–15 Ma, whereas the emergence of antlers with coronet was concomitant with the second increase in seasonality associated to the cooling ca. 15–13 Ma.

KEYWORDS:

• Cervidae
• evolution
• antler
• palaeohistology
• palaeophysiology

Acknowledgments

We thank Isaac Casanovas-Vilar for the map of Figure 1 and for magnetostratigraphic data. We also thank the CT SCAN lab of the Museo Nacional de Ciencias Naturales de Madrid (MNCN), for the CT scans; the ICP Preparation & Conservation Area for tireless preparation of the fossils; and Loïc Costeur (Naturhistorisches Museum Basel, Switzerland) for access to specimens of Chilleurs-aux Bois under his care. We also thank two anonymous reviewers for their suggestions and constructive comments on a previous version of this paper.

This work is dedicated to Prof. Jorge Morales, for his enormous contribution to the field of Miocene mammals and in gratitude for having promoted ruminant research in Spain making us part of it. Jorge, you have been an exemplary mentor and a great friend over the years, sharing with us your passion for fossils and forming a great team of people who love their work. We are extremely lucky and very proud to be part of your research lineage.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This publication is part of projects PID2020-116220GB-I00 and PID2020-117289GBI00 funded by MCIN/ AEI/10.13039/501100011033/,with funding also by the Government of Aragon (Research Group ref. E33_20R).